Other than relatively slow speed vehicles, e.g. vehicles such as conventional tractors which are capable of road speeds up to a maximum of 50 kph, have been required by safety legislation in some countries to have a steering system which is mechanical in nature, although this may be power assisted. Thus in the event of power failure, the vehicle may still be steered. The legislation in at least some countries is or has been modified, such that hydraulic steering systems may be used, but only provided that there is some back-up facility for achieving steering in the event of steering system hydraulic component failure. Such legislation has applied to vehicles such as tractors, which are capable of road speeds of say, up to 80 kph. Hence higher speed tractors necessarily have been provided with mechanical, power assisted steering systems.
Conventional slower speed vehicles which are intended to be driven off-road e.g. during tractor working operations, have traditionally been provided with steering systems which are hydraulic in nature, including hydraulic actuators to swivel wheels of the vehicle to achieve steering. Mechanical and hydraulic steering systems have different characteristics. Operators tend to prefer hydraulic steering when driving such vehicles off-road.